when does it grow back its branches and turn green?
You are outside of their natural growing zone. Even mulching will not be enough to sustain them outdoors through the winter. This will have to be grown as a container species in your area, so that it can be brought in during the colder portions of the year. With this being said, the shrub is probably dead. You can check by cutting back anything that is brittle, until you come to an are that is alive, or green inside. If there is still life, then there is still a chance for survival. If the entire thing is brittle, then it is likely dead.